1. Field of the Invention
This invention relates to polymeric condensation products for restorative dentistry. More particularly, it relates to polymeric condensation products useful as a component of filled resin composites. Depending on filler content, such filled resin composites may be used as crown and bridge materials, either with or without an alloy substrate; or as reconstructive materials, bioprostheses, restorative materials, filling materials, inlays, onlays, laminate veneers, and the like. The polymeric condensation products of the present invention have improved water sorption characteristics and excellent wear resistance.
2. Brief Description of the Related Art
In recent years, materials used for dental restorations have comprised principally acrylate or methacrylate polymers. Typical acrylate resinous materials are disclosed in U.S. Pat. No. 3,066,112 to Bowen, U.S. Pat. No. 3,179,623 to Bowen, U.S. Pat. No. 3,194,784 to Bowen, U.S. Pat. No. 3,751,399 to Lee et al. and U.S. Pat. No. 3,926,906 to Lee et al. An especially important methacrylate monomer is the condensation product of bisphenol A and glycidyl methacrylate, 2,2'-bis [4-(3-methacryloxy-2-hydroxy propoxy)-phenyl]-propane (hereinafter abbreviated "BIS-GMA"). Polyurethane dimethacrylates (hereinafter abbreviated to PUDMA) are also commonly-used principal polymers in dental restorative materials of this type.
Since BIS-GMA is highly viscous at room temperature, it is generally diluted with an acrylate or methacrylate monomer having a lower viscosity such as trimethylol propyl trimethacrylate, 1,6-hexanediol dimethacrylate, 1,3-butanediol dimethacrylate, and the like. Other dimethacrylate monomers, such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate and tetraethylene glycol dimethacrylate, are also in general use as diluents.
When these acrylic resinous materials were first developed, they were used for dental restorative purposes unfilled, that is, without the presence of any other organic or inorganic component. However, because acrylic materials exhibit high coefficients of thermal expansion relative to the coefficient of thermal expansion for the tooth structure, these unfilled substances proved to be less than satisfactory. The disparity in thermal expansion, coupled with high shrinkage upon polymerization, resulted in poor marginal adaptability and ultimately led to secondary decay. Furthermore, the wear and abrasion characteristics and the overall physical, mechanical and optical properties of these unfilled acrylic resinous materials were quite poor. Composite dental restorative materials containing methacrylate resins and fillers were thus developed, the fillers generally comprising inorganic materials based on silica, silicate glass, or quartz.
There are now available materials which exhibit high diametral tensile strength, excellent optical properties and polishability, and low water sorption while at the same time complying with all of the requirements specified in ADA Specification No. 27 for Direct Filling Resins. Particularly suitable restorative materials include the compositions having improved inorganic filler materials such as those disclosed in commonly assigned U.S. Pat. No. 4,547,531 to Waknine, disclosing self-curing two-component compositions, and U.S. Pat. No. 4,544,359 to Waknine, disclosing visible light curable compositions.
Other monomers and polymers particularly suited for dental restorative resins and other dental applications are disclosed in commonly assigned U.S. Pat. No. 5,276,068 to Waknine and U.S. Pat. No. 5,444,104 to Waknine. Such materials make use of a novel polycarbonate dimethacrylate which is the condensation product of two parts of hydroxyalkylmethacrylate of the formula H.sub.2 C.dbd.C(CH.sub.3)C(O)O--A--OH, in which A is a C.sub.1 -C.sub.6 alkylene, and 1 part of a bis(chloroformate) of the formula ClC(O)--(OR).sub.n --OC(O)Cl, in which R is a C.sub.2 -C.sub.5 alkylene having at least two carbon atoms in its principal chain, and n is an integer in the range from 1 to 4. Where no diluent monomer is used, this novel polycarbonate dimethacrylate is reacted in an amount of about 65-75% by weight of the total resin composition with a secondary monomer in an amount of about 25-35% by weight of the total resin composition. Suitable secondary monomers include BIS-GMA, PUDMA, and the like. Alternatively, where a diluent monomer is used, the novel polycarbonate dimethacrylate is present in an amount of about 30-80%, with 5-60% of a secondary monomer and 1-50% of a diluent monomer. This polycarbonate dimethacrylate imparts excellent strength to the cured resin, but it is somewhat costly.
Thus, despite recent advances in the development of filled dental restorative materials having led to composites having higher resistance to abrasion, better handling characteristics, and more satisfactory visual appearance, there remains a need for improvement in the wear resistance of filled compositions used as crown and bridge materials and denture-base materials. Improved water sorption in particular would contribute to the long-term stability of a restoration and is particularly desirable.